Communications Networks


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Communications Networks

  1. 1. Chapter 2 Communications Networks
  2. 2. Introduction <ul><li>Topics </li></ul><ul><ul><li>Telephony Networks </li></ul></ul><ul><ul><li>OSI Reference Model </li></ul></ul><ul><ul><li>The Internet </li></ul></ul><ul><ul><li>Asynchronous Transfer Mode Networks </li></ul></ul><ul><ul><li>Networking Components </li></ul></ul><ul><ul><li>Network Topologies </li></ul></ul>
  3. 3. Introduction <ul><li>A network is a group of computers that can communicate with each other so they can share information </li></ul><ul><li>When computers can communicate with each other they can share resources </li></ul><ul><li>When a server provides a resource for a client to access, this is referred to as a shared resource </li></ul>
  4. 4. Telephony Networks <ul><li>IP telephony networks make better use of available bandwidth </li></ul><ul><li>VoIP network carries voice traffic cheaper than a switched circuit telephone network </li></ul>
  5. 5. Telephony Networks <ul><li>In a PSTN, a dedicated end-to-end circuit is allocated for each call </li></ul><ul><li>In a VoIP network, data is much more compressed and carried in packets </li></ul>
  6. 6. The OSI Model <ul><li>An architecture that allows the devices of different manufacturers to work together to communicate with different operating systems </li></ul><ul><li>This architecture determines how hardware, software, topologies and protocols exist on the network and how they operate </li></ul>
  7. 7. The OSI Model <ul><li>Physical layer </li></ul><ul><ul><li>Defines mechanical, functional, procedural and electrical aspects of networking </li></ul></ul><ul><ul><li>Includes connectors, circuits, voltage levels and grounding </li></ul></ul>
  8. 8. The OSI Model <ul><li>Data Link layer </li></ul><ul><ul><li>Converts data from upper layers into logical packages or frames </li></ul></ul><ul><ul><li>Converts logical frames into raw bits that are transmitted by the Physical layer </li></ul></ul>
  9. 9. The OSI Model <ul><li>Network layer </li></ul><ul><ul><li>Provides connectivity and path selection between two systems </li></ul></ul><ul><ul><li>routing and addressing layer </li></ul></ul>
  10. 10. The OSI Model <ul><li>Transport layer </li></ul><ul><ul><li>Provides a virtual end-to-end connection so that data transferred between two hosts will arrive without errors and in the correct order </li></ul></ul>
  11. 11. The OSI Model <ul><li>Session layer </li></ul><ul><ul><li>Allows two applications on different computers to establish dialog control </li></ul></ul><ul><ul><li>Regulates which side transmits </li></ul></ul><ul><ul><li>Determines the time and length of the transmission </li></ul></ul>
  12. 12. The OSI Model <ul><li>Presentation layer </li></ul><ul><ul><li>Translates data from the Application layer into an intermediary format </li></ul></ul><ul><ul><li>Provides services such as data encryption, and compresses data </li></ul></ul>
  13. 13. The OSI Model <ul><li>Application layer </li></ul><ul><ul><li>Provides application programs access to print and file services to ensure that effective communication with other application programs is possible </li></ul></ul>
  14. 14. Data Encapsulation
  15. 15. The Internet <ul><li>The Internet was originally called ARPANET </li></ul><ul><ul><li>Developed by the Department of Defense to provide a way to connect networks </li></ul></ul><ul><li>Internet is a network of interconnected, yet independent networks </li></ul><ul><li>The language of the Internet is TCP/IP </li></ul>
  16. 16. Asynchronous Transfer Mode (ATM) Networks <ul><li>ATM uses connection-oriented switches to permit senders and receivers to communicate by establishing a dedicated circuit </li></ul><ul><ul><li>Data travels in fixed 53-byte cells </li></ul></ul><ul><ul><li>Five bytes are used for header information and 48 bytes are used for data </li></ul></ul><ul><ul><li>Data transfer rate can reach up to 9,953 Mbps </li></ul></ul>
  17. 17. Networking Components <ul><li>Baseband uses a digital transmission pulse at a single fixed frequency </li></ul><ul><ul><li>Entire bandwidth of the cable is used to transmit one data signal </li></ul></ul><ul><ul><li>Limits any cable strand to either half duplex or full duplex </li></ul></ul>
  18. 18. Networking Components <ul><li>Broadband uses analog transmission over a continuous range of values </li></ul><ul><ul><li>Travels one way only in optical waves </li></ul></ul><ul><ul><li>Necessary to have two channels, one for receiving and one for sending data </li></ul></ul><ul><ul><li>More than one transmission can operate on a single cable </li></ul></ul>
  19. 19. Networking Components <ul><li>Media: Cables and Wireless </li></ul><ul><ul><li>Coaxial cable was the first type of cable used to network computers </li></ul></ul><ul><ul><li>Coaxial cables are made of a thick copper core with an outer metallic shield used to reduce external interference </li></ul></ul><ul><ul><li>Twisted pair cable comes in seven different categories. </li></ul></ul>
  20. 20. Networking Components <ul><li>Media: Cables and Wireless </li></ul><ul><ul><li>Twisted-pair cabling is either unshielded (UTP) or shielded (STP) </li></ul></ul><ul><ul><li>Fiber was designed for transmissions at higher speeds over longer distances </li></ul></ul><ul><ul><li>Fiber uses light pulses for signal transmission, making it immune to RFI, EMI, and eavesdropping </li></ul></ul>
  21. 21. Networking Components <ul><li>Media: Cables and Wireless </li></ul><ul><ul><li>Wireless network refers to technology that allows two or more computers to communicate using standard network protocols, but without network cabling </li></ul></ul><ul><ul><li>Wireless networking hardware requires the use of technology that deals with data transmission over radio frequencies </li></ul></ul>
  22. 22. Networking Components <ul><li>Media: Cables and Wireless </li></ul><ul><ul><li>Most widely used wireless standard is the IEEE 802.11 standard </li></ul></ul><ul><ul><li>The IEEE standards for wireless are 802.11a and 802.11b </li></ul></ul>
  23. 23. Networking Components <ul><li>A hub is a multiport repeater that retransmits a signal on all ports </li></ul><ul><ul><li>Operates at Layer 1 of the OSI model </li></ul></ul><ul><ul><li>Can connect segments or a network </li></ul></ul><ul><ul><li>Cannot segment a network </li></ul></ul>
  24. 24. Networking Components <ul><li>A bridge can connect two different types of topologies </li></ul><ul><ul><li>Does not understand anything above the Data Link layer </li></ul></ul><ul><ul><li>Moves data more rapidly </li></ul></ul><ul><ul><li>Takes longer to transmit because it analyzes each packet </li></ul></ul>
  25. 25. Networking Components <ul><li>Switches operate at the Data Link layer of the OSI model </li></ul><ul><ul><li>Packet forwarding decisions are based on MAC addresses </li></ul></ul><ul><ul><li>Determines from a physical address (MAC address) which device a packet is intended for and switches it out toward that device </li></ul></ul>
  26. 26. Networking Components <ul><li>Routers operate at the Network layer of the OSI model </li></ul><ul><ul><li>Forwards information to its destination on the network or the Internet </li></ul></ul><ul><ul><li>Routers maintain tables that are checked each time a packet needs to be redirected from one interface to another </li></ul></ul>
  27. 27. Networking Topologies <ul><li>All devices on the network compete for access on a single shared piece of media </li></ul><ul><li>Only one device can transmit or talk on the media at a time while all others must listen </li></ul><ul><li>When more than one device simultaneously tries to talk, there is competition for access to the media resulting in a collision of information </li></ul>
  28. 28. Networking Topologies <ul><li>Bus topology: </li></ul><ul><ul><li>Consists of computers connected by a single cable called a backbone </li></ul></ul><ul><ul><li>All the computers share in its capacity </li></ul></ul><ul><ul><li>Simplest method for connecting computers </li></ul></ul><ul><ul><li>10Base2 or10Base5 cable is used </li></ul></ul><ul><ul><li>The more devices, the slower the network </li></ul></ul>
  29. 29. Networking Topologies <ul><li>Ring topology: </li></ul><ul><ul><li>Consists of each computer, connects directly to the next one in line, forming a circle </li></ul></ul><ul><ul><li>Data travels in a clockwise direction and each machine accepts the information intended for it </li></ul></ul><ul><ul><li>Passes on the information that is for other machines </li></ul></ul>
  30. 30. Networking Topologies <ul><li>Ring topology: </li></ul><ul><ul><li>Uses a token, which is actually a small packet, to send information </li></ul></ul><ul><ul><li>Every computer in the ring is responsible for either passing the token or creating a new one   </li></ul></ul>
  31. 31. Networking Topologies <ul><li>Peer-to-peer network: </li></ul><ul><ul><li>All machines are equal </li></ul></ul><ul><ul><li>Each can act as a server and a client </li></ul></ul><ul><ul><li>There is no central control over shared resources </li></ul></ul><ul><ul><li>Individual users decide what to share and with whom </li></ul></ul><ul><ul><li>Less secure than a server based network </li></ul></ul>
  32. 32. Networking Topologies <ul><li>Star topology: </li></ul><ul><ul><li>Computers are connected to a centralized hub by a cable segment </li></ul></ul><ul><ul><li>Require more cabling than ring or bus topologies </li></ul></ul><ul><ul><li>One computer connection goes down, it does not affect the rest of the network </li></ul></ul><ul><ul><li>Much easier to move computers around or connect them to other networks </li></ul></ul>
  33. 33. Networking Topologies <ul><li>Mesh topology: </li></ul><ul><ul><li>All devices are connected to each other more than once to create fault tolerance </li></ul></ul><ul><ul><li>A single device or cable failure will not affect the performance </li></ul></ul><ul><ul><li>More expensive </li></ul></ul><ul><ul><li>Requires more hardware and cabling </li></ul></ul>
  34. 34. Networking Topologies <ul><li>Star bus topology: </li></ul><ul><ul><li>Computers are connected to hubs in a star formation and then the hubs are connected via bus topology </li></ul></ul><ul><ul><li>More expensive to implement </li></ul></ul><ul><ul><li>Longer distances can be covered </li></ul></ul><ul><ul><li>Networks can more easily be isolated </li></ul></ul>
  35. 35. Networking Topologies <ul><li>Star ring topology: </li></ul><ul><ul><li>Data is sent in a circular motion around the star </li></ul></ul><ul><ul><li>Eliminates the single point of failure that happens in a ring topology </li></ul></ul><ul><ul><li>Uses token passing data transmission with the physical layout of a star </li></ul></ul>